I am unable to understand why acids are converted into anhydrides on heating ?

Carboxylic  acids  molecules undergo dehydration on heating by nucleophilic  addition and elimination reaction.This results in formation in anhydride. Check attached file for the mechanism:
In our question adipic acid is dicarboxylic acid (Hexanedioic acid)and undergoes same mechanism intramolecular .
Answer should be C

Thanks for explaining with the help of mechanism.